For me, it’s Billy Bat (Naoki Urasawa).
I’ll try not to repeat my answer from previous, similar threads.
This time, I would recommend Chiyo Kuno the Psychic. The manga is short and sweet, and the couple is cute.
It’s too late to save this series since it was already axed, but the series that I wish more people had read to keep it alive is Love After World Domination.
Ayakashi Ko is a cute slice of life manga about a girl that can see spirits.
Helck is a fantasy manga that starts off with the human hero Helck competing for the title of Demon King.
My personal underrated favorites are:
For me it’s got to be Skip and Loafer. It has the most human characters I’ve seen in a manga, which makes every character interaction a delight.
I feel like Wotakoi does not enough attention. I also think Murcielago is a blast, but I don’t hear much about it from others.